Methylphenidate is a known drug (although it is a controlled substance). It is used primarily to treat hyperactive children.
Methylphenidate is a chiral molecule. The properties of the enantiomers have been investigated to some extent, although the drug is still administered as the racemate. It is generally thought that dtmp is the active material, and that its antipode (ltmp) is metabolized more rapidly.
Methylphenidate is often administered in conjunction with other drugs. It is known that the concurrent administration of two drugs that act or are metabolised through the same metabolic pathway can block that pathway, leading to drug interaction.
Racemic methylphenidate is known to interact clinically with a variety of drugs, such as the tricyclic antidepressants (TCAs), necessitating reduction in the TCA dosage when co-administered to prevent drug interaction (Physicians Desk Reference, Guide to Drug Interactions, 1994).
It is generally believed that the separate enantiomers of chiral therapeutic drugs exhibit different toxicological profiles, with one usually being the main cause of the toxic effects of drug interactions; see Ariens, Schweiz. Med. Wochenschr. 120(5):131-134 (1990). The basis for this is that each enantiomer will exhibit different preferences for the pathways or enzyme metabolism, e.g. the cytochrome P450 pathways, and therefore co-administered drugs are blocked at different sites of metabolism.